1. Field of the Invention
The present invention relates to apparatus for use in the installation of electomagnetic fields for traffic measurement and control purposes within a roadway. More particularly, this invention pertains to a mobile unit for installing circular traffic detector loops.
2. Description of the Prior Art
The traffic detector loop is in common usage for measuring and controlling roadway traffic flows. The loop or coil functions as a component of a tuned circuit. A flow of current through the conductive loop(s) produces a radiation pattern that interacts with metal objects, such as passing automobiles that detune the tuned circuit. The inductance of the coil or loop causes the flow of current therein to respond to the passage of the automobile and such variation in the flow is sensed by electrical measuring and/or control apparatus linked thereto.
The usefulness of detector loop information for controlling lights and studying traffic patterns follows, for example, from the presence of more than 250,000 light controlled intersections in congested Southern California roadways. Presently, as many as twenty-five (25) loops are in use at some intersections.
The loops are installed in both concrete and asphalt roadways. Each loop comprises an approximately one-half inch diameter conductor. The conductor is positioned in a one and one-half to three inch deep trough and is covered with a bituminous or soft epoxy sealant.
At the present time, the troughs for the loops are formed by sawing eight sided figures into the roadway with planar flat saws. Such a process is inefficient in terms of both labor cost and speed. More significantly, the resultant shape of the loop produced is inherently inappropriate for reliable detection of traffic. The corners of the octagonal shape are insensitive to flow as a result of static interference between the fields that surround the intersecting segments.